https://en.wikipedia.org/wiki/Paternity_fraud
One study, which published a rate near 30%, was performed on populations in which the purported father already suspected that he was not the genetic parent, rather than on a fully random population.[5] Studies ranging in date from 1991 to 1999 quote the following incidence rates: 11.8% (Mexico), 4.0% (Canada), 2.8% (France), 1.4% and 1.6% (UK), and 0.8% (Switzerland).[4] These numbers suggest that the widely quoted and unsubstantiated figure of 10% of non-paternal events is an overestimate. However, in studies that solely looked at couples who obtained paternity testing because paternity was being disputed, there are higher levels: an incidence of 17% to 33% (median of 26.9%).[6][7][8] Most at risk were those born to younger parents, to unmarried couples and those of lower socio-economic status, or from certain cultural groups.[6]
The article wikipedia cites has a math error: https://www.theguardian.com/politics/2008/aug/01/freedomofinformation.childprotection
I think. Read it carefully.